What will this workshop cover?

The goal of this session is to get to started using RStudio, learn how to use variables and solve basic calculations in R. We will cover:

Information on how the session is run

One hour exercise based session with tutor support. You will be given example code for a problem, then given a related exercise to complete.

Why this style?

  • Online training is tiring so keeping the sessions to one hour
  • No or limited demonstrations provided in order to provide more real world experience - you have a problem and you look up how to solve it, adapting example code
  • Trainer support to guide through process of learning

We will be working in pairs:

  • One shares the screen and the other requests remote control.
  • Take turns on who types for each exercise.
  • Share markdown file at end of session via chat
  • If possible have your camera on when doing the paired work.

What to do when getting stuck:

  1. Ask your team members
  2. Search online:
  • The answer box on the top of Google’s results page
  • stackoverflow.com (for task-specific solutions)
  • https://www.r-bloggers.com/ (topic based tutorials)
  1. Don’t struggle too long looking online, ask the trainer if you can’t find a solution!

Why R

R is a popular language, especially in data science, this can be seen in the TIOBE Index for August 2020.

It has lots of strengths:

Introduction to RStudio

RStudio by default has four main quadrants as shown below. The layout is customisable, as is the background.

When you load RStudio the syntax editor will not be open. Try and open one just like as shown below.

Using R markdown

For these workshops we will be using R Markdown. It allows you to have text (with simple formatting) and chunks of R code.

To run code in a code chunk either press the green play button or press Ctrl + Enter (or Cmd + Enter on Mac).

Using R as a calculator

We can use R to do simple or advanced calculations for us. Remember to run the code press the green play button or press Ctrl + Enter (or Cmd + Enter on Mac).

7 * 6
## [1] 42
5 / (2^2)
## [1] 1.25
(16 - 4) + (1 * 9)
## [1] 21

Exercise (R as calculator)

Use R to work out the following arithmetic:

  1. 44 * 26
  2. 9.6/1.6
  3. (12+4)^2
  4. (4*9)/(5+6)
  5. (22/36) * 100
  6. The remainder of 55 / 2 (hint: look up r’s modulus operator)
# type your code here

Assigning variables

A variable is a named storage of information. In our case today we are storing numbers.

We can assign variables by using <-. You should see the variable appear to your right in the global enviroment once you’ve run this command.

height <- 155

We can then print the output of the variable by typing in its name.

height
## [1] 155

Task

When calling a variable, be careful to type it exactly (you can also copy it or use code completion to help).

Try calling the height variable, but spell it incorrectly. You should get an error with something like Error: object ‘hieght’ not found

# type incorrect height call here

Example

We can do calculations on these variables, just as we did before. We first assign the variables, then use them in the calculation.

# test scores
Score1 <- 42
Score2 <- 92
Score3 <- 68
# average score calculation
AveScore <- (Score1+Score2+Score3)/3
# print average score
AveScore
## [1] 67.33333

You will have noticed the hashtags (#) with text in the above example. These are called comments. In later R sessions we will use a lot of comments to tell us (and others) what each line or section of code is doing.

# this is a comment

Reassigning variables

You can also change the value of a variable you have already assigned. Here we are going to add our new pay check to our previous bank balance.

Run this code to test it out:

# create variables
BankBalance <- 100
PayCheck <- 250
# add old bank balance and pay check, assigning result to bank balance
BankBalance <- BankBalance + PayCheck
# print bank balance
BankBalance
## [1] 350

Task

Try and add another pay check of £50 to the bank balance variable.

  1. Make a variable called PayCheck2 with a value of 50
  2. Assign BankBalance, and calculate BankBalance + PayCheck2
  3. Print the outcome

hint: if this doesn’t work run the code chunk above

# Reassigning variables task

Exercise 1 (Assigning variables)

Use R to work out a body mass index (BMI) of someone who is 79kg, and 1.77m tall.

  1. Assign the variables of weight and height
  2. Assign the variable of BMI, and calculate the BMI based of the weight and height variables
  3. Print the outcome
  4. Add comments on what each line of code is doing
# Exercise: BMI calculation

Exercise 2 (Assigning variables)

Debug the code below that is finding the weighted average of a students coursework and exam scores. You should find three errors:

  • logic (maths) error
  • syntax error
  • naming error
# Exercise: weighted average debugging
exam1 <- 52
coursework1 <- 82
exam2 <- 78
coursework2 < 48

cw_weight <- 0.4
ex_weight <- 0.6

course1 <- (exam1 * ex_weight) + (coursework * cw_weight)
course2 <- (exam2 * ex_weight) + (coursework2 * cw_weight)

overall_grade <- (course1 + course2)/3

overall_grade

Exercise 3 (Salary calculation)

Robin and Charlie are a married couple, one gets paid an hourly rate, the other has an annual salary. They want to workout how much annual salary they have combined before tax. Out of interest Charlie also wants to know what her hourly rate is before tax.

They used simple calculations using the following formulas:

(number hours worked per week x hourly rate) x number of weeks worked = annual salary (annual salary ÷ number of weeks in a year) ÷ hours worked per week = hourly rate

Re-arrange the code so the calculations run. You should have both the combined salary and Charlies hourly rate calculations printed.

# weeks in year
weeksYear <- 52

# Charlies hourly rate
Charlie_HourlyRate <- (Charlie_annualSary / weeksYear)/Charlie_hoursPerWeek
Charlie_HourlyRate

# salaries
Robin_HourlyRate <- 16.5
Charlie_annualSary <- 31800

# Combined salaries
CombinedSalaries <- Robin_annualSalary + Charlie_annualSary
CombinedSalaries

# Robins annual salary
Robin_annualSalary <- (Robin_hoursPerWeek * Robin_HourlyRate) * Robin_weeksWorking

# hours worked
Robin_hoursPerWeek <- 25
Robin_weeksWorking <- 48
Charlie_hoursPerWeek <- 35

Final task - Please give us your individual feedback!

This is the first time that we are exploring a remote learning format for our workshops and we would be grateful if you could take 2 mins before the end of the workshop to get your feedback!

https://lse.eu.qualtrics.com/jfe/form/SV_77M35cq1arxNcj3?course=D025-R1NV&topic=R&cohort=LT21&link=https://lsecloud.sharepoint.com/:u:/s/TEAM_APD-DSL-Digital-Skills-Trainers/EVT6p9EbxI1IjJZs_L-6ltEBuDwbhnaQoSBXI3S9Cvk6jw?e=x7izX8

The solutions we be available from a link at the end of the survey.

Individual (take home) coding challenge

A take home coding task for you.

Task: Splitting a Pizza Pilgrims restaurant bill between 3 friends; Roger, Amal and Genevieve.

  1. Make a variable for each friend that is the sum of their order (e.g. Roger would be 11 + 2)
  2. Make a variable for the shared food
  3. Make a variable called TotalBill, and calculate their total bill
  4. For those that shared food, add the shared food to their bill
  5. Comment your code
  6. Print the total bill and what each friend owes
# individual coding challenge